Prismatic font accessing in phototypesetters

ABSTRACT

An optical system for a phototypesetting machine wherein a rotating type font having at least two spaced apart rows of characters has a focused light source periodically pulsed to direct a light beam through a translucent character in each of the two rows. An optical path for each of the character images is provided through a fixed projection lens onto a predetermined portion of a photosensitive medium. A rhomboid optic element having a predetermined index of refraction is selectively interposed in either of two positions in the optical paths of the character images. In one position, the first character is blocked and light from the second character passes through the prismatic element and is sharply focused by the projection lens on the photosensitive medium. In the alternate position, the second character is blocked and light from the first character is allowed to pass directly into the projection lens to also form a sharply focused image on the medium without passing through the rhomboid element.

United States Patent Herden [451 Oct. 17, 1972 [54] PRISMATIC FONT ACCESSING IN PHOTOTYPESETTERS [72] Inventor: Robert B. Herden, Webster, N.Y.

[73] Assignee: The Singer Company [22] Filed: March 18, 1971 [21] Appl. No.: 125,747

[52] US. Cl ..95/4.5 R, 350/6, 350/285 [51] Int. Cl. ..B4lb 13/00 [58] Field of Search ..350/6, 7, 285, 204, 171; 95/4.5; 178/76 [56] References Cited UNITED STATES PATENTS I 2,767,628 10/1956 l-Iigon'net ..95/4.5 R 3,552,827 6/1971 Linde ..350/171 3,601,467 8/1971 Wildhaber ..178/7.6 2,951,428 9/1960 I-Iigonnet ..95/4.5 R

FOREIGN PATENTS OR APPLICATIONS 856,897 4/1940 France ..350/204 Primary Examiner-David Schonberg Assistant Examiner-Michael J. Tokar Attorney-George W. Killian, Patrick J. Schlesinger, Charles R. Lepshinsky and Jay M. Cantor [5 7 ABSTRACT An optical system for a phototypesetting machine wherein a rotating type font having at least two spaced apart rows of characters has a focused light source periodically pulsed to direct a light beam through a translucent character in each of the two rows. An optical path for each of the character images is provided through a fixed projection lens onto a predetermined portion of a photosensitive medium. A rhomboid optic element having a predetermined index of refraction is selectively interposed in either of two positions in the optical paths of the character images. In one position, the first character is blocked and light from the second character passes through the prismatic element and is sharply focused by the projection lens on the photosensitive medium. In the alternate position, the second character is blocked and light from the first character is allowed to pass directly into the projection lens to also form a sharply focused image on the medium without passing through the rhomboid element.

PATENTEDDL'T 17 I972. 3 9 297 INVENTOR. ROBERT B. HERDEN AGE/VT PRISMATIC FONT ACCESSING IN PI-IOTOTYPESETTERS BACKGROUND OF THE INVENTION This invention may find particular utility in the Graphic Arts industry and more particularly, in Photocomposing machines. An optical system is disclosed for projecting an image at a predetermined location on an image plane with the object selectively chosen from first or second positions in an object plane. The system automatically compensates for the difference in path length between the image plane and the two object positions in the object plane.

The use of Photocomposing machines is well known in the Graphic Arts industry. Such machines typically employ a constantly rotating film font from which a desired character is selected and projected to the image plane. In order to double the number of available characters without changing film fonts, it is known to provide a second set of characters on the film font and provide a mechanical means for shifting the film font so that the second set of characters is in position for projection to the image plane. Such mechanical shifting tended to be slow and could sometimes cause character misalignment. An alternate technique was the shifting of the image plane and/or the lens. But this too caused speed reductions and alignment difficulties. The present invention provides the desired advantage of the second set of characters but eliminates the difficulties of the shifting of the heavy mechanical parts by providing the introduction of a new small, lightweight optical element which may be easily and quickly shifted to permit selection between the two sets of characters on the film font. The invention is especially advantageous in systems which do not use a human operator, but rather use an encoded input. In such systems, font row shifting may be associated with a specific access code.

BRIEF DESCRIPTION OF THE DRAWING The features which characterize the invention are shown in the drawing wherein:

FIG. 1 is a partially broken away perspective view of a portion of a phototypesetting apparatus in accordance with one embodiment of the present invention; and

FIG. 2 is a cross section of the essential optical elements of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A variety of phototypesetting machines have been used in the Graphic Arts industry for many years. Examples are mentioned in the 1916 edition of Typographical Printing-Surfaces by Legros and Grant. In a typical phototypesetting application, the characters and/or symbols are arranged in some convenient sequence, as transparent areas, on a film font. The film font is appropriately positioned and optical elements are located between the film font and the photosensitive medium on which the selected characters are to be serially recorded. In order to record the character on the photosensitive medium, a shutter is opened and/or a light is flashed which allows the image from the film font to be recorded on the photographic medium. The high speed shutter, or the brief duration of the light flash, limits the distortion of the image on the photographic medium to an acceptable level.

Many improvements on the basic phototypesetting machine have been made to provide a variety of features and improved and faster operation. In some phototypesetters, the lens may be moved to position the selected character at the desired location on the photographic medium; while in other machines, the photographic medium may be moved in order to have the desired portion thereof in the image zone. Other improvements include the control of phototypesetters by perforated tape and/or computers.

In order to increase the operating speed of phototypesetters, it is known to provide a film font which rotates constantly at a high speed and which includes timing signals and other control marks for determining the instantaneous position of the film font so that a high speed lamp may be flashed at the instant that the desired character is in the required location for projecting the image thereof on the photographic medium.

In typical applications, the film font may comprise a disc with the characters disposed in a ring near the outer perimeter of the disc. An alternate type of film font employs an endless belt with the characters arranged side by side along the belt. It is obvious that if the number of characters is increased, the length of the belt must be correspondingly increased and/or the radius of the disc must be increased. Furthermore, it is obvious that when such increases are made, in order to accommodate a font 'with a larger number of characters, that the cycle time from any given character in the font to the same given character will be increased unless there is an increase in velocity.

It was evident at an early stage in the development of phototypesetting machines that advantages might be obtained by providing more than one ring of characters on the disc, or more than one row of characters about the belt, and providing means for shifting the film font so that the characters of the selected ring on the disc, or row on the belt, could be placed in the required location for projecting the image thereof onto the photographic medium. In spite of the obvious advantages of the techniques just described, there are related disadvantages which have limited commercial acceptance of the technique.

Satisfactory and economical optical means had not been found for shifting from one portion of a film font to another. More specifically, it was difficult and expensive to maintain an accurate and sharp focus of the object on the photographic medium when the object plane was not always at a uniform distance from the image plane. That is, images from different locations in an object plane could be projected to a common area in an image plane but this would either involve two separate lens systems or a technique for refocusing the lens if only a single lens was employed. In order to show the manner in which the present invention overcomes this problem, more specific reference is now made to the drawing.

In FIG. 1, 101 represents a film font. This font is made up of one or more sections which, in effect, form an endless belt which is securely, but interchangeably, attached to a rotating wheel 102. The wheel 102 rotates about a center (not shown) such that the successive characters on the film font may be sequentially presented at a predetermined point hereinafter called the object plane. For convenience of illustration, the film font 101 is illustrated as having only an upper case R and a lower case r. In actual practice, the film font 101 would include a complete set of alphanumeric symbols and/or other characters as may be required in the same row with both the upper case R and the lower case r. As a matter of fact, in a practical application, a given row of alphanumeric characters would normally include both the upper case and lower case characters, and the characters in the other row would be similar except that they might be either bold face or italic face characters. Any other arrangements which suits the convenience of the user could be arranged. For convenience in nomenclature, the row of characters that includes the upper case R will be referred to as the upper row, while the row of characters that includes the lower case r will be referred to as the lower row.

The film font 101 includes timing marks 103 which may be used in a manner which is well known to those skilled in the phototypesetting arts for providing a signal indicative of the instantaneous position of the film font 101. To assist in providing the signal indicative of the instantaneous position of the film font 101, a light source 105 and a light sensor 106 are provided.

By means of an optical system which will be described more fully hereinbelow, the character image on film font 101 will be projected to the photosensitive medium 110. Subsequent to the projection of the image from the film font 101 to the photosensitive medium 110, the said medium 110 will be advanced upward as shown by the arrow near the photosensitive medium 110 and by an amount which is a function of the size of the projected image. In a subsequent cycle of operation, another character will be selectively projected from either the upper or lower rows of the film font 101 to the photosensitive medium 110. In this manner, a sequence of characters which form a message may be projected onto medium 110.

When the film font 101 is instantaneously at the desired position for projecting the desired character therefrom to the photosensitive medium 110, a flash lamp 111, such as a pulsed xenon flash tube, may be flashed. The light from the flash lamp 111 is transmitted through the transparent portion 119 or 120 of the opaque film font 101 representing the selected character and the image thereof is projected on the photosensitive medium 110. Although the film font 101, together with the wheel 102, is in continuous rotation, the duration of the flash of lamp 111 is so short that there is no objectionable blurring of the image projected to the photosensitive medium 110. The detailed techniques for providing this facility are not new to those familiar with the phototypesetting art and therefore, are not included herein. Suitable electrical connections may be made to flash lamp 111 and light source 105 at terminals 111T and 105T.

Included in the optical path between the flash lamp 111 and the photosensitive medium 110 is an optical condenser 112, and a projection lens 113. The projection lens 113 may be mounted on a turret (not shown) together with one or more other projection lens (not shown) such that by rotating the turret to place a selected projection lens in the optical path, the degree of magnification of the character from the film font 101 onto the photosensitive medium may be selected. That is, by selecting an appropriate projection lens 113, the image of the character selected from the film font 101 on the photosensitive medium 110 may be of any desired size. By techniques which do not form a part of the present invention, the photosensitive medium 110 will be caused to advance, after each exposure, an amount which is appropriate for the combination of the image transmitted from the film font 101 and the projection lens 113 which was used.

In addition to the projection lens 113, another optical element hereinafter called a rhomb may be selectively included. As will be explained more fully hereinafter, when the rhomb 116 is in a first or upper position, it acts as a shutter to block the transmission of light from the upper row of film font 101 to the projection lens 1 13 and the photosensitive medium 110. Conversely, when the rhomb 116 is in a second or lower position, it acts as a shutter to block the transmission of light from the lower row of the film font 101 to the projection lens 113 and the photosensitive medium 110. When the rhomb 116 is in the first or upward position to block the upper row of the film font 101, the light which is transmitted from the flash lamp 111 through the translucent character of the lower row of film font 101 (in the illustration r) passes through projection lens 113 without being effected by any of the optical properties or characteristics of the rhomb 116. Conversely, when the rhomb 116 is in the second or lower position, the light transmitted from the flash lamp 111 through the character in the upper row of the film font 101 (in the illustration R) is transmitted through the rhomb 116 and the projection lens 113 to the photosensitive medium 110. It is important to note that the optical path between a character in the upper row of film font 101 and the photosensitive medium 110 is greater than the optical path between a character in the lower row of film font 101 and the photographic medium 110. Such conditions would normally cause one of the images at the photosensitive medium 110 to be out of focus if the other image is in focus. That is, although the horizontal distances between the upper and lower row of the film font 101 and the plane of the photosensitive medium 110 are equal, the image from the upper rail must be projected downwards a distance equal to the separation between the upper and lower rows. This downward projection may be more clearly seen in FIG. 2, wherein it will be seen that the image from the upper row of film font 101 is reflected from rhomb surface 117 through the rhomb 116 to rhomb surface 118 where it is reflected through projection lens 113. The vertical distance between rhomb surface 117 and rhomb surface 118 is exactly equal to the displacement between the upper and lower rows of the film font 101. As a consequence, the rays of light which exit from the rhomb 116 are in the same position they would be in if the character were being projected from the lower row of film font 101.

The foregoing may be better understood by a consideration of the following principles.

In the structure of the present invention, the dimensions of the rhomb 116 and the index of refraction thereof are selected so as to accommodate to the increased object conjugate path length to the upper font row without an attendant change in location, magnification, or focus condition in the image plane. That is, without any change in the image conjugate path. Moreover, it is a necessary condition that the reflections restore the image attitude to match that of the non-reflected lower font row. A rhomb will provide these characteristics.

As is well known to those familiar with optical principles, if a projection lens is positioned between an object plane and an image plane and these elements are so positioned that an object in the object plane is in focus at the image plane, the image will go out of focus if the object plane is moved away from the projection lens. With the object plane moved away from the projection lens, it would be necessary to move the image plane towards the projection lens in order to have the image in sharp focus. In summary, if the object plane is moved away from the projection lens, the image plane must be moved closer to the projection lens in order to maintain a clear and sharp focus. Conversely, if the object plane is moved closer to the projection lens, the image plane must be moved away from the projection lens in order to maintain clear and sharp focus.

It is also a well known optical principle that when an object plane and an image plane are positioned with a projection lens therebetween in such a manner that there is a clear image on the image plane of an object in the object plane the image will be thrown out of focus when a piece of clear glass with optically flat sides is inserted between the object plane and the projection lens. As is known, moving the image plane away from the projection lens will restore the original and sharp focus. The change in the plane of focus of the image is a result of a physical characteristic of the piece of glass that was inserted between the object plane and the projection lens. The distance that the image plane would have to be moved away from the projection lens in order to obtain a clear and sharp image is a function of the thickness of the inserted glass and the characteristic of the glass known as its index of refraction.

Considering now the two optical principles just discussed, it should be noted that when the object plane is moved away from the projection lens, the image plane would be moved towards the projection lens in order to maintain a sharp focus; and that when a piece of glass is inserted between the object plane and the projection lens the image plane must be moved away from the projection lens in order to maintain a sharp focus. Accordingly, it would be possible to introduce a piece of optically flat glass between the object plane and the projection lens and then to move the object plane away from the projection lens by a critical amount such that a sharp image may be produced on the image plane. That is, the insertion of the glass would have necessitated the movement of the image plane away from the projection lens in order to maintain a sharp focus; and the movement of the object plane away from the projection lens would have required movement of the image plane towards the projection lens. However, it is possible to maintain a fixed relationship between the projection lens and the image plane even though the effective distance between the object plane and the projection lens, such that the change introduced by the addition of the glass exactly compensates for the change introduced by the movement of the object plane.

It should also be noted that if the distance between the image plane and the projection lens were changed, the degree of magnification would be altered. That is, if it is necessary to change the relationship between the projection lens and the image plane, the magnification of the image plane will be altered.

Expressing these same principles a little bit differently, it is possible to maintain a fixed distance between the projection lens and the image plane, even though the object plane may be moved, if a piece of glass having the required dimensions and index of refraction is introduced between the object plane and the projection lens. That is, if an object plane is moved away from the projection lens and away from the ideal position of the object plane with respect to a fixed relationship between the projection lens and an image plane, a correction may be made by the insertion of an appropriate piece of optically flat glass. That is, so far as the projection lens and the image plane are concerned, the motion of the object plane and the introduction of the compensating glass has resulted in no net change.

Considering now more specifically the structure of the photocomposing machine including the present invention, it will be seen that for a variety of reasons, it is highly desirable to maintain the distance between the projection lens 1 13 and the photosensitive medium at a fixed distance.

Considering now FIG. 2 and the film font 101; the area designated represents the area which may be occupied by one of the characters in the upper row of film font 101; (the capital R as illustrated in FIG. 1). The upper and lower limits of this character are designated as 120U and 120L, respectively. That is, no character in the upper row of film font 101 will have any portion which extends above the limits of 120U nor any portion which extends below the limits of 120L. In

a similar manner, the characters of the lower row of film font 101; (lower case r in the illustration of FIG. 1); are confined in area 119 between the upper limit 119U and the lower limit 1191.. The total distance between corresponding points in areas 119 and 120 will be the distance X as shown in FIG. 2. That is, the distance X is the distance between the upper limit 120U and the upper limit 119U; or the distance between the lower limit 120L and the lower limit 119L.

With the rhomb 116 situated as illustrated in FIG. 2, the vertical distance between the rhomb surfaces 117 and 118 (i.e., the surfaces are inclined to the horizontal) is the distance Y. The rhomb 116 is selected such that the distance Y is equal to the distance X. The inclined surfaces 117 and 118 of the rhomb 116 are normally silvered so that they are reflecting surfaces. Accordingly, when the rhomb 116 is in the position as shown in either FIGS. 1 or 2 and the flash lamp 111 is flashed, light will be transmitted through the transparent area 120 of film font 101 to project an image of the character (upper case R in the illustration of FIG. 1) onto the rhomb surface 117. The image on surface 117 is then reflected to surface 118 and projected through projection lens 113 to the photosensitive medium 110. By means of the rhomb 116, the image of the upper case R in the upper row of film font 101 is projected through the projection lens 113 in exactly the same manner that a character in area 119 would be projected from the lower row of film font 101 through the projection lens 113 if the rhomb 116 were moved away. It should be apparent from the foregoing discussion that the area 120 is further away from the projection lens 113 than the area 119 by a distance equal to the distance X which in turn is equal to the distance Y. As indicated, it is necessary that the distance Y, which is the vertical distance between the inclined planes 117 and 118 of the rhomb 116, is exactly equal to the distance between corresponding points of the areas 119 and 120 on the film font 101. The thickness T of the rhomb 116 and the index of refraction of the rhomb 116 are carefully chosen so that the effective optical path increase of the glass of the rhomb 116 exactly compensates for the increase in the distance between the projection lens 113 and the area 120 over the distance between the projection lens 113 and the area 119.

In practical applications, the projection lens 113 would normally comprise a compound lens. In addition, the projection lens 113 might be mounted on a turret (not shown) such that any one of a plurality of projection lens 113 could be positioned in the optical path. By providing a plurality of projection lenses 113, it would be possible to provide different degrees of magnification, and/or reduction, or the image on the film font 101, onto the photosensitive medium 110.

In a practical and economical application of the invention to a phototypesetter, it is desirable to use a rhomb 116 which is a commercial item available from suppliers and/or manufacturers of such goods. Accordingly, commercial rhombs having a dimension Y which falls within an allowable range are tentatively selected. Then by means of standard formulas which are known to those skilled in the necessary arts, calculations may be made to determine a particular rhomb whose dimension Y, thickness T, and index of refraction are such that a sharp image may be obtained on an image plane when the relationship between the image plane and the projection lens is fixed and an image of an object in an object plane is projected from the object plane to the image plane without the use of the rhomb and when an object at a second location on the object plane is projected to the image plane with the use of the rhomb.

In practical applications, the projection lens 113 would normally comprise a compound lens. In addition, the projection lens 113 might be mounted on a turret (not shown) such that any one of a plurality of projection lens 113 could be positioned in the optical path. By providing a plurality of projection lenses 113, it would be possible to provide different degrees of magnifications, and/or reduction, or the image on the film font 101, onto the photosensitive medium 110.

In a practical and economical application of the invention to a phototypesetter, it is desirable to use a rhomb 116 which is a commercial item available from suppliers and/or manufacturers of such goods. Accordingly, commercial rhombs having a dimension Y" which falls within an allowable range are tentatively selected. Then by means of standard formulas which are known to those skilled in the necessary arts, calculations may be made to determine a particular rhomb whose dimension Y, thickness T, and index of refraction are such that a sharp image may be obtained on an image plane when the relationship between the image plane and the projection lens is fixed and an image of an object in an object plane is projected from the object plane to the image plane without the use of the rhomb and when an object at a second location on the object plane is projected to the image plane with the use of the rhomb.

As illustrated most clearly in FIG. 2, when the rhomb 116 is in the lower position, the supporting structure for the rhomb 116 includes a shutter area 123 which is non-reflecting and which blocks any light transmitted from the flash lamp 111 through the area 119. Conversely, when the rhomb 116 is in a raised position, the shutter area 123 blocks anylight transmitted from the flash lamp 111 through the area 120. Accordingly, when the rhomb 116 is in its lower position, characters from the upper row of film font 101 may be transmitted through the rhomb 116 and the projection lens to the photosensitive medium and when the rhomb 116 is in an upper position, characters from-the lower row of film font 101 may be projected through the projection lens 1 13 to the photosensitive medium 110.

Solenoid structure provides a suitable means for selectively moving the rhomb 116 between its upper and lower limits. The solenoid 131 is mounted on a solenoid frame 132 which is fixed relative to the projection lens 113, the photosensitive medium 110, and the frame (not shown) on which the wheel 102 and other components are mounted. The frame 132 also supports pivot 133 on which bell crank 134 may be pivoted. The bell crank 134 will be pivoted on pivot 133 in response to the actuation, or deactuation, of solenoid 131 which will move the solenoid plunger 135 between two limits. When the bell crank 134 is pivoted clockwise as seen in FIG. 1, the rhomb actuating am 136 will be moved downward and position the rhomb 116 as shown in FIGS. 1 and 2. The rhomb actuating arm 136 and the ball crank 134 are coupled at pivot 137. The assembly is such that the entrance face 122 of rhomb 116 is parallel to the plane of the photosensitive medium 110 at the time that the rhomb 116 is in its lower position. The solenoid 131 may be selectively energized by any of the well known techniques. By use of the structure described, it is possible to project characters from first and second rows of a film font to a selected area of an image plane. It is obvious that the concept could be expanded by using a second rhomb which is below the rhomb 116 and which could be used to project characters located in a third row of a film font 101 onto the photosensitive medium 110 wherein the third row of characters is located below the two rows indicated in FIGS. 1 and 2.

Numerous advantages may be obtained by incorporating this invention into a phototypesetting machine. For example, for a given film font character size the total number of available characters may be doubled or even tripled without any increase in the radius of the wheel 102. In addition, the cited increase in the availability of characters is achieved without any need to make periodic adjustments of the relationship between the projection lens and the image plane or between the projection lens and the object plane.

An alternate structure could be made wherein it is desired to selectively project an image of an object in an object plane to first or second areas in an image plane. In such a case a rlfimb of suitable proportions and index of refraction could be inserted between the image plane and the projection lens. With the rhomb in the first and second selected positions, the image of the object would be projected to first and second areas, respectively, of the image plane.

While there has been shown and described what is considered at present to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the embodiment shown and described, and it is intended in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a phototypesetting machine of the type described, the combination comprising:

a. an opaque type font having upper and lower portions and arranged to be continually moved past a predetermined object position as an annular belt, said type font being provided with a plurality of transparent characters in said upper and lower portions so that when a light beam is directed toward the object position of the type font, character images from said upper and lower portions will appear on the other side of the font in an image plane;

b. a light source intermittently energized to provide a light beam which covers both the upper and lower portions of the type font at a predetermined object position;

0. a photosensitive medium spaced from and positioned parallel to the type font for receiving a character image thereupon in a predetermined character position and adapted for movement in a plane parallel to the object plane but constrained against other movement;

d. a projection lens fixedly positioned between the object plane of the font and the photosensitive medium and arranged to receive a character image projected through the type font and to focus a sharply defined character image on the predetermined character portion of the photosensitive medium; and

e. an optic element having at least two interior reflecting surfaces adapted to be adjustably interposed between the object plane of the type font and the projection lens in first and second positions, in the first position the optic element directs a character received from one portion of the font, in the second position the optic element allows a character from the other portion of the font to pass directly to the projection lens and blocks a character from the portion of the font which had been directed to the lens in the first position.

2. The combination of claim 1 wherein the index of refraction of the optic element is selected and two interior reflecting surfaces of the element are spaced apart a predetermined distance in order that the character received from the type font by the element and directed through the projection lens to the position on the photosensitive medium forms a sharply defined image.

3. The combination of claim 2 wherein the characters provided in the upper and lower portions of the t e font are rran ed in s aced a art r ws.

t. The corn ination of cfaim 3 \iihere fn the reflecting surfaces of the optic element are positioned at a fortyfive degree angle with respect to the image plane of the photosensitive medium and the difference in imaging lens object conjugate caused by the insertion of the optic element in the optical path of a character is equal to the distance between the two reflecting surfaces in a plane parallel to said image plane.

5. The combination of claim 1 wherein the horizontal optical path of a character image received from one portion of the type font and directed through the projection lens to the photosensitive medium is equal to the horizontal optical path of a character image that emanates from the other portion of the type font and which passes directly through the projection lens to the photosensitive medium when the optic element is in said second position.

6. The combination of claim 5 further including selectively energizable electromagnetic means to move the optic element to the first or second positions. 

1. In a phototypesetting machine of the type described, the combination comprising: a. an opaque type font having upper and lower portions and arranged to be continually moved past a predetermined object position as an annular belt, said type font being provided with a plurality of transparent characters in said upper and lower portions so that when a light beam is directed toward the object position of the type font, character images from said upper and lower portions will appear on the other side of the font in an image plane; b. a light source intermittently energized to provide a light beam which covers both the upper and lower portions of the type font at a predetermined object position; c. a photosensitive medium spaced from and positioned parallel to the type font for receiving a character image thereupon in a predetermined character position and adapted for movement in a plane parallel to the object plane but constrained against other movement; d. a projection lens fixedly positioned between the object plane of the font and the photosensitive medium and arranged to receive a character image projected through the type font and to focus a sharply defined character image on the predetermined character portion of the photosensitive medium; and e. an optic element having at least two interior reflecting surfaces adapted to be adjustably interposed between the object plane of the type font and the projection lens in first and second positions, in the first position the optic element directs a character received from one portion of the font, in the second position the optic element allows a character from the other portion of the font to pass directly to the projection lens and blocks a character from the portion of the font which had been directed to the lens in the first position.
 2. The combination of claim 1 wherein the index of refraction of the optic element is selected and two interior reflecting surfaces of the element are spaced apart a predetermined distance in order that the character received from the type font by the element and directed through the projection lens to the position on the photosensitive medium forms a sharply defined image.
 3. The combination of claim 2 wherein the characters provided in the upper and lower portions of the type font are arranged in spaced apart rows.
 4. The combination of claim 3 wherein the reflecting surfaces of the optic element are positioned at a forty-five degree angle with respect to the image plane of the photosensitive medium and the difference in imaging lens object conjugate caused by the insertion of the optic element in the optical path of a character is equal to the distance between the two reflecting surfaces in a plane parallel to said image plane.
 5. The combination of claim 1 wherein the horizontal optical path of a character image received from one portion of the type font and directed through the projection lens to the photosensitive medium is equal to the horizontal optical path of a character image that emanates from the other portion of the type font and which passes directly through the projection lens to the photosensitive medium when the optic element is in said second position.
 6. The combination of claim 5 further including selectively energizable electromagnetic means to move the optic element to the first or second positions. 